The invention relates to a process making it possible to connect an electric cable having a core made from a light metal such as aluminium and covered with an insulating sleeve, to a standardized end element such as a connector contact. The invention also relates to a connecting part usable in performing this process.
The invention is applicable to all industries using long electric cable lengths and for which cost and weight savings are desired. One of these industries is the aeronautical industry.
In the manufacture of aircraft, certain large section, copper core cables more particularly equipping the main electric power supply circuits have been replaced over the past few years by aluminium core cables. Despite the need of using larger section aluminium core cables in order to compensate a reduced conductivity compared with copper, the mass or weight balance reveals a gain of approximately 50%.
In order to take further advantage of the weight gain resulting from the use of aluminium core cables, it would also be logical to replace smaller section copper core cables by aluminium core cables. This replacement is more particularly envisaged for cables ranging from gauge 10 (section 4.9 mm.sup.2) to gauge 24 (section 0.2 mm.sup.2).
However, although the ultimate tensile strength difference between the two materials causes no particular problems in the case of cables having a cross-section exceeding 5 mm.sup.2, it becomes critical for cables with a smaller cross-section. Thus, the stresses exerted on the cable, particularly during the construction of cable systems, may then be prejudicial to the electrical continuity of the circuits and therefore to the safety of aircraft.
In the case of smaller size cables from gauge 10 to gauge 24, to obtain a mechanical strength for the connections produced with aluminium core cables substantially equivalent to that obtained with copper core cables it becomes necessary for the insulating sleeve of the cable, which is made from plastic materials having high mechanical and electrical performance characteristics, to participate in the strength of the connection.
Moreover, unlike copper core cables, the sensitivity of aluminium core cable to chemical attack, requires the connection between the aluminium cable and the copper contact to be made tight, in order to insulate the aluminium from the ambient medium.
However, in view of the larger diameter needed for the aluminium core cable compared with the copper core cable, any diameter increase to the contacts for ensuring the sealing and the tensile strength of the connection makes it difficult or even impossible to use standardized tools for the fitting and unlocking of the contacts, if use is made of the most widely employed standardized connectors with unlocking of the contacts from the rear.
In addition, an increase to the diameter of the cavities formed on the standardized connectors for receiving the standardized contacts is difficult to envisage without modifying the location of the cavities, as a result of their proximity on existing connectors. However, a modification to the positions of the cavities would make obsolete all the presently used standardized connectors.
Finally, a change to the connection technology for using contacts with unlocking from the front would require significant modifications and the creation of new connectors, which is obviously undesirable.